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Abstract

 

(Begin page 1945)

AAPG Bulletin, V. 85, No. 11 (November 2001), P. 1945-1966.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

The effects of salt evolution, structural development, and fault propagation on Late Mesozoic-Cenozoic oil migration: A two-dimensional fluid-flow study along a megaregional profile in the northern Gulf of Mexico Basin

S. Cheree Stover,1 Shemin Ge,2 Paul Weimer,3 Barry C. McBride4

1Hydrogeology Group, Department of Geological Sciences, University of Colorado, Boulder, Colorado, 80309-0399; email: [email protected]
2Hydrogeology Group, Department of Geological Sciences, University of Colorado, Boulder, Colorado, 80309-0399; email: [email protected]
3Energy Minerals and Applied Research Center, Department of Geological Sciences, University of Colorado, Boulder, Colorado, 80309-0399; email: [email protected]
4AEC Oil & Gas (USA) Inc., 370 17th Street, Suite 3050, Denver, Colorado, 80202; email: [email protected]

AUTHORS

Cheree Stover received a bachelor's degree in earth and planetary sciences from Harvard University (1993). After graduating, she spent three years as a hydrogeologist with Arthur D. Little. She earned an M.S. degree in geology from the University of Washington (1998) and a Ph.D. in geology from the University of Colorado (2001). Her dissertation topic is "Fluid flow and sediment deformation in the evolution of sedimentary basins: One-dimensional application to Woodlark Basin, Papua New Guinea, and two-dimensional application to the northern Gulf of Mexico Basin."

Shemin Ge earned a Ph.D. from the Johns Hopkins University in 1990, an M.A. degree from the University of British Columbia in 1985, and a B.S. degree from Wuhan University of Technology of China in 1982. Ge worked for Papadopulos and Associates from 1989 to 1993 and later joined the University of Colorado, where she is currently an associate professor. Ge's research focuses on fluid-flow related geologic processes in a variety of geologic environments.

Paul Weimer holds the Bruce D. Benson Endowed Chair in Petroleum Geology in the Department of Geological Sciences at the University of Colorado at Boulder and is director of the Energy and Minerals Applied Research Center. His research interests are in sequence stratigraphy, reservoir geology, and petroleum systems of deep-water continental margins.

Barry C. McBride received a B.S. degree from Furman University (1985), an M.S. degree from Western Michigan University (1988), and a Ph.D. from the University of Colorado at Boulder (1997). He has worked as an exploration geologist with Mobil Exploration and Production U.S. Inc., Mobil Global Interpretation Support, and HS Resources, Inc. and as a geologist with CogniSeis Development Inc. He is now an exploration geologist with AEC Oil & Gas (USA) Inc. working the Rocky Mountains.

We thank the following companies and their representatives for support and informative input as part of the 1999 Gulf of Mexico research consortium at the University of Colorado: AGIP, Amerada-Hess, Amoco, Anadarko, BHP, BP, Burlington Resources, Consolidated Natural Gas, Conoco, CXY Energy, Enterprise, Exxon, LL&E, Marathon, Maxus Energy, Mobil, Occidental, Phillips, Shell, Spirit Energy 76, Texaco, Union Pacific Resources, and Vastar. We extend special thanks to Platte River Associates, especially Jay Leonard, China Leonard, Charly James, and Tom Schutter, for generous use of their modeling software. This research was funded in part by a National Science Foundation Graduate Research Traineeship grant and the support of the Gulf of Mexico research consortium at the University of Colorado.

ABSTRACT

Sequential two-dimensional (2-D) forward modeling of fluid flow along a north-south, 600 km megaregional cross section across the northern Gulf of Mexico Basin illustrates the influence of structural, stratigraphic, and thermal evolution on oil generation patterns and migration paths. Twelve megaregional fluid-flow models, which span from the Late Cretaceous to the Holocene, were constructed for this study. Each model uses a sequential structural restoration and proprietary well data to constrain the structural and stratigraphic development of the study area and to calibrate production depths along the megaregional profile. These fluid-flow models specifically address the levels of influence that salt evolution, sedimentation, thermal history, and fault development induce on temporal oil migration patterns.

Results from the sequential 2-D fluid-flow models across the northern Gulf of Mexico Basin indicate that allochthonous salt evolution and excess-pressure development from differential sedimentation strongly influenced Late Mesozoic-Cenozoic oil migration patterns along the entire megaregional profile. Within the lower slope part of the profile, early and fairly rapid maturation of source rocks was accompanied by slow elevation of excess pressures. As a result, oil migration in these regions was minimal, and the impact of salt evolution on the fluid flow was restricted to circulatory patterns at the base of salt stocks. Within the center of the profile (Begin page 1946) (offshore Louisiana shelf), however, the evolution of allochthonous salt and the formation of high excess pressures, coeval with the development of listric and normal faults, strongly impacted the oil migration patterns. Penetration of high excess-pressure regimes by both listric and normal faults directed fluid flow vertically upward along the fault systems. Upon encountering salt sheets, oil migration in these regions exhibited both divergent and convergent flow patterns, flowing laterally along the base of the salt. A similar scenario was observed in the northern part of the profile (southern onshore Louisiana), reflected by oil migration beneath the Terrebonne salt sheet. Upon evacuation of allochthonous salt in the central and northern regions of the profile, migration patterns were primarily lateral. When excess pressures in these regions exceeded 50 MPa, however, oil flowed vertically through the salt welds and along suprasalt faults. A more localized and well-constrained study of fault migration in the Oligocene-Miocene detachment province further suggests that faults are important factors as migration pathways, with episodic flow directing oil migration into observed shallow reservoirs.

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